Removal of fluorine from water



Patented Apr. 10, 1945 REMOVAL OF FLUORINE FROM WATER- Robert J. Myers,Rydal, and- Donald S. Herr, Philadelphia, Pa., assignors to The ResinousProducts & Chemical Company, Philadelphia, Pa., a corporation ofDelaware No Drawing. Application June 24, 1942, Serial No. 448,329

14 Claims. (01. 21o 24) This invention deals with the removal of smallamounts of fluorine in the form of its compounds from water contaminatedtherewith in order to render the water harmless.

The harmful effects of water supplies containing small amounts offluorine compounds are well known. It has been established, however,that reduction of fluorines to about 1 P. P. M. orless from waterotherwise potable renders the treated water flt for various industrialuses, fit for human consumption and without danger of causing defects inbones or teeth.

The problem of reducing the fiuorine'content of water has beenapproached in various ways. It has been proposed, for example, that thisb- Jectionable component be precipitated, but the least soluble fluorideis still soluble above the limit tolerated by human beings. It has alsobeen proposed that water be desalted by proper use of base exchangers intheir hydrogen form followed by so-called anion exchangers. This methodis needlessly uneconomical in nature, since the usual salt content ofwater is unobjectionable. It has also been proposed to reduce fluorideconcentrations by selective sorption on the surface of a solid.

While previously suggested sorption methods have definite advantagesover the other named methods, the method here described has manyadvantage over other sorption methods and meets the requirements for anideal procedure of removing fluorides from water. The desirablecharacteristics for the process are (1) very low solubility of purifyingagent or agents in water, (2) large effective surface area for speedingup the process, (3) freedom from formation of colloidal material inwater, (4) retention or improvement of potability of water, (5) economyof operation,-

(6) ease of control of operation, (7) possibility of continuou ratherthan batch-wise operation, and

(8) repeated regeneration of the absorbing agent to a state of highactivity.

Previously proposed sorptive agents have failed in one or more of theabove requirements, some disintegrating too readily, others wasting awayrapidly on regeneration or not returning to their original activity onregeneration, While still others lack the capacity, efliciency, oreconomy necessary for the purification of large volumes of water in aneconomic manner.

It i an object of this invention to provide a method which meets theabove requirements for a process for the removal of fluorine in the formbest results are obtained when sufficient acid is of its compoundsdissolved in water. It is also an object to reduce the fluoride contentof otherwise potable water below one part per million. It is also anobject to absorb fluorides selectively without introducing solublereagents. It is a further object to treat water at the pHs normallyencountered in water supplies without requiring or causing violentchanges in pH.

It has been found that these objects are accomplished by contacting afluorine-containing water with an anion exchange resin which has beenimpregnated with an aqueous solution of an aluminum salt.

As an anion exchange resin there may be used the insolubilized resinresulting from the reaction of diamino benzenes, particularly metaphenylene diamine, and formaldehyde, or the reaction of amethylol-forming phenol, formaldehyde, and a primary or secondarynon-aromatic amine, particularly polyalkylene polyamines, or thereaction of ketones or polyhalides with polyalkylene polyamines, orreaction involving a combination of the various above mentionedmaterials. The preparation of particularly effective and eflicientresins suitable for so-called anion exchange or, more strictly speaking,the absorption of acidic constituents from fluids is described inapplications Serial Nos. 387,679; 387,683; 387,684; 387,685; 387,686;387,687 and 387,688 filed April 9, 1941. The resins there described aregelled and heat-hardened phenol-formaldehyde type resins havingaminomethyl substituents of the phenyl nuclei.

In order to render these resins effective for the removal of fluorinefrom compounds thereof from water the resin in a granular form isimpregnated with an aqueous solution of an aluminum salt. It is thendesirable to rinse the impregnated resin to free it from solution ofsalt prior to treatment of fluorine-containing water. If desired,rinsing may be done with a portion of fluorine-containing water whichmay be discarded before the bulk of the water to be treated is contactedwith the impregnated resin, or desalted water may desirably be used.

For the optimum use of the anion exchange resins it is desirable thatfree, flocculent hydrated alumina 'is not formed as the result of freealkali on the resin. It is, therefore, desirable to rinse the anionexchange resin thoroughly before impregnation is performed or better totreat the resin with a very dilute solution of an acid. The

used to convert about 1% to the acid form before aluminum salt.

to about 6% of the resin impregnation with the After the resin has beenproperly prepared, it is contacted with the fluorine-containing water.This may be done by stirring the resin with a batch of water andseparating resin and treated water. A more eflicient method, however, isto flow the fluorine-containing water through a bed of the treatedanion-exchange resin. When the treated resin has become saturated withfluorine, it is readily regenerated by treatment with an alkalinesolution, such a an aqueous solution of sodium hydroxide, ammoniumhydroxide, sodium carbonate, or the like. The regenerant solution may beconcentrated for recovery of its fluorine content. The resin may then berinsed, treated with a dilute solution of an acid, such as hydrochloric,sulfuric, acetic, etc., subjected to the action of an aluminum salt, andused again for the removal of fluorine. Thus, the anion exchange aesinsare capable of repeated use and regenera- In treating the resin with analuminum salt solution it is preferable to treat the resin by upflow,because the solution of aluminum salt causes a considerable and rapidincrease in volume of the resin. Other operations are performed ingeneral equally well by either upflow or downflow. As an aluminum saltthere may be used a sulfate, chloride, nitrate, acetate, or othersoluble salt, including alums. The concentration of salt is notseemingly of particular importance. Solutions f 2% to are particularlyconvenient and economical to use.

Additional details will be evident from the following descriptions ofspecific applications of aluminum-treated anion exchange resins to theimprovement of fluorine-containing water. A one inch glass column wasfilled with about 250 ml. of a resin prepared by reacting phenol,formaldehyde, and tetraethylene pentamine to form a gel and then dryingthe gel at 125 C. The resulting insoluble resin was crushed to a /40mesh size before being placed in the column. The column was then floodedwith a solution containing 500 P. P. M. of hydrochloric acid. There wasthen poured through the column a 5% solution of aluminum sulfate, whichwas then drained from the column. After a single rinse to remove excessaluminum solution a water containing 107 parts per million of fluorideion was passed through the column downflow at a rate of 2 gallon persquare foot per minute. Samples were taken until the effluent gave atest for fluorine. Up to this point 7500 ml. of water had been obtainedwhich gave a completely negative test for fluorine. This exampledemonstrates the sharp break-through which is characteristic of theanion exchange resins impregnated with aluminum salts.

The capacities of various typ s of exchange materials were compared inthe following way. Samples of waters were prepared containing 50, 25,and 10 P. P. M. of fluoride ion as sodium fluoride and divided into 100ml. lots. Various materials were then treated with a 4% solution ofcommercial aluminum sulfate, rinsed with desalted water, and dried. Lotsof 0.200 g. were weighed out and placed in the 100 ml. portions of theprepared solutions. The solutions with treating agents were stirred andafter two hours were examined for changes in fluoride content by acolorimetric method using zirconyl salts and alizarin red. Capacitiesfor absorption of F- were then calculated in milligrams of F" per gramof dry treated resin. An aluminum treated synthetic gel zeolite absorbed4.8, 1.8, and 1.8 mgm. per g. for the 50, 25, and 10 P. P. M. solutionsrespectively. Sample of an aluminum-treated sulfonated coal absorbed10.8, 5.7, and 3.2 mgm. per g. for the 50, 25, and 10 P. P. M. fluoridesolutions respectively. Comparable figures for a specially preparedtrlcalcium phosphate were 7.2, 5.1, and 3.6 mgm. per g. respectively.The highest absorptive capacity in this series of tests was shown by agelled, insolubilized, and aluminum salt treated resin from phenol,formaldehyde, and triethylene tetramine, for which the absorptivecapacities were 13.8, 9.2, and 5.7 mgm. per g. for the solutionscontaining 50, 25, and 10 P. P. M. of fluoride ion respectively. Thesuperior capacity of tile absorbents of this invention is plainly evidenA gelled and insolubilized anion exchange resin from the reaction ofmetaphenylenediamine and formaldehyde was treated with a 10% solution ofaluminum sulfate and rinsed. A solution con taining 40 P. P. M. of F assodium fluoride was then passed downflow over 100 cc. of the resin untilfluorides appeared in the eilluent. The apparent capacity of this resinwas about 1100 grains F per cu. ft.

A gelled and heat-hardened resin made from phenol, formaldehyde, andtriethylene tetramine and granulated to a 20/30 mesh size was placed ina one inch column. A 4% solution of aluminum sulfate was passedtherethrough, after which the column was rinsed with water desalted bypassage through a base exchanger in its hydrogen form followed by ananion exchange resin. Thereupon water containing 500 P. P. M. of F waspassed through the column downflow and tests made for fluoride ion foreach 250 ml. passed therethrough. After 1250 ml. had been treated, therewas still no fluorine in the water but after 1500 ml. of water had beentreated, the effluent contained 5 P. P. M. of fluoride, while after 1750ml. had been treated, the eilluent contained 35 P. P. M. of fluoride.With complete removal of fluoride the aluminum treated anion exchangeresin absorbed over 1200 grains of fluoride ion per cubic foot. The pHof all samples of water tested remained close to 7%.

When the resin in the column had been saturated with fluorine, the resinwas reconditioned by washing with a 4% solution of sodium carbonate. Itwas noted that this treatment removed both fluorine and aluminum fromthe resin, but the rate of fluorine removal was much more rapid thanthat of aluminum. The resin was given a rinse with water, then with alittle dilute hydrochloric acid, and again with water. The column wasthen flooded with a 4% solution of aluminum sulfate and rinsed. Theresin was again used for removing fluorine from water with the same endresult, namely, a capicity of over 1200 grains of fluoride ion per cubicfoot. It is interesting to note that for a bed volume of 250 ml. all ofthe absorbed fluorine can be removed with less than two liters'of a 4%solution of soda ash and that the capacity for absorption is retained onrepeated regeneration and reuse.

In order to emulate actual field conditions Philadelphia tap water wasfortified with 6.5 P. P. M. of fluoride ion by addition of an equivalentamount of sodium fluoride. This water was passed downflow through asmall column packed with 226 ml. of a resin like that used immediatelyabove. The rate of passage was 5 gallons per square foot per minute witha time of retention in the column of three to four minutes. The first 99liters of effluent were entirely free of fluorine, while after 119liters had passed, the efliuent contained less than two parts permillion of fluoride ion and did not exceed a fluoride content of 2 P. P.M. until after 159 liters had passed through the column. Duringv thetreatment of this water samples were examined from time to time forchloride and sulfate content. It was found that the chloride ionconcentration decreased slightly at first-and tended to increaseslightly after prolonged use of the resin. The concentration of sulfateion, however, tended to increase somewhat at the start, since aluminumsulfate had been used to treat the resin. The eflluent was foundpalatable and potable and the greater part of the effluent examined wasat or below the limit of safety for human use.

By methods generally similar to those described there have been studiedanion exchange resins activated for selective fluorine absorption with.

2% to 5% solutions of aluminum chloride, aluminum nitrate, ammoniumalum, and aluminum sulfate. In every casealuminum was taken up by theresin as established by actual analysis. The aluminum appeared to befirmly bound and to show an absorption capacityfor fluorine roughly inproportion to the aluminum content of the resin. Resins treated with thevarious salts were tested with a synthetic water made up from distilledwater to contain nitrate at 6 P. P. M., chloride at 30 P. P. M., sulfateat 120 P. P. M., bicarbonate at 400 P. P. M. and fluoride at P. P. M.The pH of this water was 8.1. Other synthetic waters were made fromdistilled water with-200 P. P. M. of CaClaZHzO, 100 P. P. M. ofMgSOflHzO, 100 P. P. M. of sodium chloride, 0.60 P. P. M. of iron, and0.38 P. P. M. of ammonia from ferrous ammonium sulfate, and variouscontrolled concentrations of sodium fluoride. The pH of these syntheticwaters was 5.9. In every instance fluoride removal took place in asatisfactory manner. The other ions were removed only to a limited'extent except for iron which was completely removed. The results showedthat the aluminum sulfate treated resins w re. somewhat superior to theresins treated with other salts, but capacities in all cases were highlysatisfactory. Further tests showed that not only may iron be removed,but also other metals yielding insoluble hydroxides, such as copper. Thesimultaneous removal of fluoride and heavy metals is of practicalimportance.

The use of aluminum-impregnated anion exchange resins for the reductionor removal of the fluorine-content of fluorine-containing waterspresents many advantages over any method heretofore proposed. By theprocess described above fluorine-containing waters are rendered potableby selective sorption of fluorine from fluorine-containing watersupplies in an economical and practical way. The insolubleanion-exchange resins, particularly those of the phenolformaldehyde typehaving aminomethyl substituents, are ideal bases for holding aluminumcompounds which may then be used to sorb the fluorine content of water.The presence of other soluble compounds than those containing fluorinedoes not interfere with the process and heavy metals are removed alongwith the fluorine.

The process is rapid because of the natureof the resin bases used andlends itself to continuous flow methods. By the use of two or morecolumns packed with anion exchange resin the removal of fluorine andregeneration may be carried on without interruption in the supply ofwater. When a bed of aluminum-treated anion exchange resin has becomesaturated with respect an aqueous solution of an aluminum salt in anamount at least sufficient to absorb the toxic concentration of saidfluorine from said water and separating from said resin the water whichhas I been contacted therewith.

2. The process of reducing the fluorine content of fluorine-containingwaters below the toxic.

limit which comprises contacting a fluorine-containing water with awater-insoluble anion exchange resin which has been impregnated with anaqueous solution of aluminum sulfate in an amount at least sufficient toabsorb the toxic concentration of said fluorine from said Water andseparating from said resin the water which has been contactedtherewith.v

3. The process of reducing the fluorine content of a fluorine-containingwater below the toxic limit which comprises contacting said water with awater-insoluble, gelled, and heat-hardened phenol-formaldehyde resinwhich has nuclear aminomethyl substituents, which is capable ofabsorbing acidic constituents from fluids, and which is impregnated withan aqueous solution of an aluminum salt in an amount at least suflicientto absorb the toxic concentration of said fluorine from said water andseparating from said resin the water which has been contacted therewith.

4. The process of reducing the fluorine content of a fluorine-containingwater below the toxic limit which comprises contacting said water with awater-insoluble, gelled, and heat-hardened phenol-formaldehyde resinwhich has nuclear aminomethyl substituents, which is capable ofabsorbing acidic constituents from fluids, and which is impregnated withan aqueous solution of aluminum sulfate in an amount at least sufiicientto absorb the toxic concentration of said fluorine from said water andseparating from said resin the water which has been contacted therewith.

5. The process of reducing the fluorine content of a fluorine-containingwater below the toxic limit which comprises contacting said water with awater-insoluble, gelled, and heat-hardened resin from phenol,formaldehyde, and a polyalkylene polyamine, said resin being suitablefor the absorption of acidic constituents from fluids and beingimpregnated while mainly in its basic form with an aqueous solution ofan aluminum salt in an amount suflicient to absorb the toxic fluorinecontent of said water, and separating from said resin the water whichhas been contacted therewith.-

'6. The process of claim 5 wherein the aluminum salt is aluminumsulfate.

'7. The process of reducing the fluorine content of afluorine-containing water below the toxic limit which comprisescontacting said water with a water-insoluble, gelled, and heat-hardenedresin from phenol, formaldehyde, and triethylene tetramine, said resinbeing suitable for the absorption of acidic constituents from fluids andbeing impregnated while mainly in its basic form with an aqueoussolution of an aluminum salt in an amount sufllcient to absorb the toxicfluorine content of said water, and separating from said resin the waterwhich has been contacted therewith.

8. The process of claim 7 wherein the alumi num salt is aluminumsulfate.

9. The process of reducing the fluorine content of a fluorine-containingwater below the toxic limit which comprises contacting said water with awater-insoluble, gelled, and heat-hardened resin from a methylol-formingphenol, formaldehyde, and a polyalkylene polyamine, said resin beingsuitable for the absorption of acidic constituents from fluids and beingimpregnated while mainly in its basic form with a 2% to 10% aqueoussolution of an aluminum salt, and separating from said resin the waterwhich has been contacted therewith.

10. A cyclic process for treating fluorine-containing water and reducingthe fluorine content thereof which comprises the steps of impregnating awater-insoluble anion exchange resin chiefly in its basic form with anaqueous solution of an aluminum salt in an amount sumcient to absorb thetoxic fluorine content of said water, contacting the resin impregnatedas aforesaid with fluorine-containing water to sorb the toxic fluorinecontent thereof on the impregnated resin, thereupomseparating the waterand the resin, treating the resin having a. sorbed fluorine content withan alkaline solution until the fluorine content is removed, andrepeating the above steps cyclically. Y

11. A cyclic process for treating fluorine-containing water and reducingthe fluorine content thereof below the toxic limit which comprises thesteps of treating a water-insoluble anion exchange resin in its basicform with a dilute solution of an acid in an amount sufilcient toconvert from about 1% to about 6% of the resin to its acid form,impregnating the treated resin with an aqueous solution of an aluminumsalt in an amount sufiicient to give capacity for absorbing the toxicfluorine content of said water, contacting the resultingaluminum-impregnated resin with the fluorine-containing water andsorbing thereon the toxic fluorine content, separating the water and theresin, treating the resin having a sorbed fluorine content with analkaline solution until the fluorine content thereof is removed, andrepeating the-above steps cyclically.

12. A cyclic process for treating fluorine-containing water and reducingthe fluorine content thereof below the toxic limit which comprises thesteps of treating a water-insoluble, gelled, and heat-hardenedphenol-formaldehyde resin which has nuclear aminomethyl substituents,which is suitable for the absorption of acidic constituents, and whichis in its basic form, with a dilute solution of an acid in an amountsufficient to convert from about 1% to about 6% of the resin to its acidform, impregnating the treated resin with an aqueous solution of analuminum salt in an amount sufficient to give capacity for absorbing thetoxic fluorine content of said water, contacting the resultingaluminum-impregnated resin with the fluorine-containing water andsorbing thereon the toxic fluorine content, separating the water and theresin, treating the resin having a sorbed fluorine content with analkaline solution until the fluorine content thereof is removed, andrepeating the above steps cyclically.

13. A cyclic process for treating fluorine-containing water and reducingthe fluorine content thereof below the toxic limit which comprises thesteps of treating a water-insoluble anion exchange resin in its basicform with a dilute solution of an acid in an amount suflicient toconvert from about 1% to about 6% of the resin to its acid form,impregnating the treated resin with a 2% to 10% aqueous solution of analuminum salt, contacting the resulting aluminum-impregnated resin withthe fluorine-containing water and sorbing thereon the toxic fluorinecontent. separating the water and the resin, treating the resin having asorbed fluorine content with an alkaline solution until the fluorinecontent thereof is removed, and repeating the above steps cyclically.

14. The cyclic process of claim 13 in which the aluminum salt isaluminum sulfate.

ROBERT J. MYERS. DONALD S. HERR.

